He's saying Yes, it would be fine to use dum.
Instead of "when you can be...", with "dum" you'd be saying "provided you can be..." You might even ask for alternative translations of "if you can be..." or "considering that you can be..." to avoid translating "when".
A less literal translation might sound more like a succinct Latin motto. "Actions speak louder than words" in Latin is "Acta, non verba", literally "Actions, not words." So to get a more Latin-sounding motto, you may want to give the translator a more telegraphic version, like "Be not normal, be yourself" or "Not normal, be you", or "Yourself, not normal" and see what you get.
Or leave it as is. People understand that the same word can have different meanings in different languages, as Americans learn when in ירושלים and looking for רחוב פינס .